Ken Macdonald, the former Director of Public Prosecutions, said on Radio 4's Today this morning that the legally recognised categories of race, religion, disability, sexual orientation and transgender identity represented "lines in the sand", because these were "crimes that threaten social cohesion as a whole and therefore national life." He was worried that extending the notion to members of other groups represented a "watering down" of the concept.

Presenter John Humphrys, in an interview with the mother of murdered goth Sophie Lancaster, seemed anxious to draw a distinction between those who were unable to "choose" what group they fell into (such as members of ethnic minorities) and those who dressed a certain way as a way of expressing their identity. Mrs Lancaster, who has campaigned tirelessly on the issue since her daughter's death in August 2007, responded that members of some subcultures often felt an inner compulsion to express themselves a certain way. This is fair enough, but side-steps the broader issue.

Confining the notion of "hate crime" to a small number of historically victimised groups, such as members of ethnic and religious minorities, is inherently misleading. It wrongly locates the source of the problem in the victim rather than in the perpetrator: in some innate or ineradicable characteristic of the person who is the target of the assault, and which therefore attracts the law's protection. But it's not because being gay is an innate characteristic (if indeed it is) that homophobic violence is a singled out for special opprobrium. It's simply that homophobia exists, and is a widespread problem, just as racism exists.

Indeed, Humphrys' suggestion amounts to victim blaming. Just because goths and other lifestylers choose to dress in a way that can attract attention from violent thugs doesn't mean that they bring crime on themselves. To tell them that they should dress differently to avoid goth-haters is no different from telling women that they should dress modestly to avoid getting raped - or, indeed, telling a Muslim woman that any Islamophobic abuse she may suffer is her fault for wearing a hijhab. Hate is hate, whatever prompts it, as the judge in the trial of Sophie Lancaster's killers recognised. Indeed, by dividing victims of hate crime into artificial bureaucratic categories (and telling others that, sorry, there's no box for you) that state doesn't just violate the principle that all are equal before the law, it also misses the point.

Whatever characteristic provokes a hate crime, whether it is genetic like skin colour, innate like sexual identity, deeply felt like religious belief or more freely chosen such as membership of a subculture, the target of hate is the same: difference. Hate crimes are crimes against diversity. They are crimes of othering, of scapegoating and stereotyping, in which the perpetrator blames others for their own inadequacy, failure or frustration. It really doesn't matter, or should not, whether the criminal in question is offended by a person's race, their dress or their perceived sexuality. Or, for that matter, by their appearance, their assumed politics or their membership of a social class or occupational group.

History suggests that the victimising of minority groups is a largely arbitrary phenomenon. Bigotry is not bigoted: it will latch on to anything or anyone capable of being perceived as marginal, though it tends to be worse at times of economic and social insecurity. The current recession has not led, as some predicted, to an epidemic of banker-bashing, but it has been accompanied by increased resentment of immigrants and welfare recipients - often with cheerleading from sections of the press. A short list of groups in modern Britain especially vulnerable to hate attacks would have to include sex workers (a category already recognised by Merseyside police but by few other forces), priests, people with mental health problems and the elderly, in addition to the racial and sexual minorities that already enjoy the explicit protection of the law.

To be fair, the government has already gone some way towards recognising the need to look at hate crime more broadly. Last year, it issued a report, Challenge It, Report It, Stop It (pdf), which stated that crimes such as the murder of Sophie Lancaster "may fall outside of the nationally monitored strands, but they are nonetheless hate crimes, and they should be treated as such." The decision by Greater Manchester Police to record such crimes is therefore less unprecedented or at variance with national policy than has been reported.

If nothing else, recording crimes against goths and members of other subcultures will enable the authorities to gauge the extent of the problem more accurately. The murder of Sophie Lancaster was unusual in its brutality, its fatal result and its apparent randomness (she and her boyfriend were attacked by a group of drunken teenagers while walking in a park) but in its wake many other goths came forward to report their experiences of verbal and physical harassment. There must be a suspicion, though, that without the efforts of the Sophie Lancaster Foundation in pushing for the recognition of anti-goth crime, and without the galvanising effect of the 2007 murder, today's announcement would not have happened. And this creates its own dangers. Simply adding another tick-box to an already substantial list won't solve the problem of a legal and bureaucratic scheme that continues to privilege some types of hate-crime as special while ignoring others.